The present invention relates to electromagnetic switches of the type having a contact spring capable of offering gimbal effect.
A known sealed type contact element is, for example, a reed switch as shown in FIG. 1. This reed switch is of the construction wherein a pair of magnetic metal reeds 101, opposite to each other, are sealed in a glass capsule 102. These reeds function both as springs to restore their contacts into their original positions and as magnetic circuits to cause their contacts to attract each other. The reed switch has been required to operate with high sensitivity. To this effect, the stiffness of the reeds should be as low as possible. One method to meet this requirement is to extend the length of the reed or to reduce the thickness of the reeds at least in part. In practice, however, the thinning of the reeds tends not only to cause the reeds to be deformed by external mechanical force but also to weaken its attractive force. While in order to minimize the size of the reed switch, it is necessary to minimize length and diameter of the reeds. This may result in making the contact force and the retractile force lower. Still further, the process of enclosing the reeds into the glass capsule accounts for a greater portion in the production of reed switches.
Another problem is that when a switch matrix is constituted of reed switch elements, the use of a large number of constituent components is required and the overall construction becomes intricate, resulting in high manufacturing cost.
Another known sealed type relay is described in the U.S. Pat. No. 3,331,040, in which the relay employs annular contacts which may be closed by a resilient diaphragm. This relay, as shown in FIG. 2, comprises a nickel-iron tube 201 provided as an inner magnetic member, a mild steel annulus 200 installed concentrically with the tube 201 and electrically insulated from the tube 201 by a glass member 202, an outer magnetic member 203 constituted of a yoke, and a disk-shaped resilient diaphragm 205 secured to the mild steel annulus 200 at its periphery by means of a metal end cap and installed opposite a cooperating end face 204 of the inner magnetic tube 201 by way of a gap. A plurality of arcuate slots 206 are disposed on the diaphragm 205 to give the diaphragm 205 suitable elasticity. The diaphragm 205 and the tube 201 are of both electrically conductive structure. Thus, when a coil 207 is energized, diaphragm 205 makes contact with the tube 201 at the end face 204.
This type of relay, however, is likely to be deformed when it is secured in position because the diaphragm 205 is supported at one side, like in a cantilever structure. Furthermore, because the diaphragm 205 is disk-shaped and hence occupies a fairly large area, the pitch between two diaphragms becomes too large when a plurality of them are disposed on a plane. Accordingly, such a relay is hardly practical for some applications, such as a switch matrix for a speech path.
Other drawbacks of the metal sealed type switch are:
a. The metal case serves as part of the signal line, causing stray capacity, which makes high speed signal transmission difficult;
b. When glass is used for insulation and sealing, the part where the glass is welded must be maintained at a high temperature for about 10 minutes, thereby raising the cost of production;
c. The high temperature required when fusing glass serves to deteriorate the magnetic characteristics of the core. For example, the magnetic characteristics of the core of Fe-Co-V medium-hard magnetic alloy will be deteriorated by about 20% in terms of residual flux and about 30% in terms of coercive force when the core is maintained at a glass fusing temperature of 650.degree. C for about 10 minutes; and
d. Because the case is made of metal, it is very difficult to realize a construction in which signal lines of a dual wire system, such as a two-wire or four-wire system, are insulated from each other and installed within one case. Accordingly, when such switch is used for a speech path in a telephone switching system, the arrays of the switch matrix becomes complicated.